Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$198.49	13.458%	$225.2028	$225.20	$225.20	$225.20
Purchase #2	$112.34	12.463%	$126.3409	$126.34	$126.35	$126.30
Purchase #3	$39.47	11.252%	$43.9112	$43.91	$43.90	$43.90
Purchase #4	$38.64	5.726%	$40.8525	$40.85	$40.85	$40.90
Purchase #5	$63.87	9.826%	$70.1459	$70.15	$70.15	$70.10
Purchase #6	$89.34	5.792%	$94.5146	$94.51	$94.50	$94.50
Purchase #7	$40.90	11.553%	$45.6252	$45.63	$45.65	$45.60
7 purchase totals =	$583.05		$646.5931	$646.59	$646.60	$646.50